Username or EmailPassword
"message size X exceeds size limit Y" is one of the more easier bounce message to understand, really.
Unfortunately there's no standard way to deliver useful bounce information to the end-client since the format of the bounce message is not standardized anywhere. This means that you end up getting free-form text bounce messages of various degree of usability. Some servers, notably qmail, even cuts the bounce short. It's pretty darn hard to parse this reliably on the client so no, machines can't easily read this.